CN113035686B

CN113035686B - Ion source, FAIMS device and method for improving resolution and sensitivity of FAIMS device

Info

Publication number: CN113035686B
Application number: CN202110233360.6A
Authority: CN
Inventors: 李华; 杜晓霞; 朱鸿成; 曾鸿达; 李明磊
Original assignee: Guilin University of Electronic Technology
Current assignee: Guilin University of Electronic Technology
Priority date: 2021-03-03
Filing date: 2021-03-03
Publication date: 2023-06-16
Anticipated expiration: 2041-03-03
Also published as: CN113035686A

Abstract

The application discloses an ion source, a FAIMS device and a method for improving resolution and sensitivity of the FAIMS device. The ion source comprises a first support body, a second support body and an air flow pipeline, wherein the first support body and the second support body are arranged at intervals to form an ion channel, the first support body is provided with a needle electrode, the second support body is provided with an annular electrode, and the tip end of the needle electrode extends into the annular electrode; the gas flow conduit is directed toward the tip of the needle electrode for introducing helium gas to the needle tip. An annular cavity surrounded by the annular electrode is used for introducing nitrogen. According to the ion source provided by the embodiment of the application, the helium environment is arranged around the tip end of the needle-shaped electrode, more ions are ionized in the helium environment, the ion concentration at the entrance of the migration zone is increased, and the ion signal intensity is increased along with the increase of the ion concentration. The ions with increased ionization are larger than the ions lost by the impact migration polar plate, so that the overall ion signal intensity is enhanced, and the resolution and the sensitivity of the high-field asymmetric waveform ion migration spectrum are improved at the same time.

Description

Ion source, FAIMS device and method for improving resolution and sensitivity of FAIMS device

Technical Field

The invention relates to the technical field of chemical detection, in particular to an ion source, a FAIMS device and a method for improving resolution and sensitivity of the FAIMS device.

Background

The high-field asymmetric waveform ion mobility spectrometry (FAIMS) is a rapid chemical detection technology developed on the basis of ion mobility spectrometry, and the mechanism is that gaseous chemical substances carried by carrier gas enter an ion source region to be ionized into charged ions, and the ionized ions can be separated under the condition of high and low electric fields due to different ion mobility, so that different substances are detected.

The carrier gas used in the FAIMS device is generally nitrogen, the carrier gases are different, the resolution ratio corresponding to the FAIMS is different, and according to the related principle, helium with lighter mass and smaller volume is doped into the carrier gas used in the FAIMS device based on the nitrogen, so that the movement amplitude of ions can be improved, and the resolution ratio is improved. However, this approach brings about a decrease in ion signal intensity while increasing resolution.

Disclosure of Invention

An object of the embodiment of the present application is to provide an ion source, a FAIMS device and a method for improving resolution and sensitivity thereof, so as to solve the technical problem that in the prior art, the resolution and sensitivity of the FAIMS device cannot be balanced, and the resolution is improved, and meanwhile, the strength of an ion signal is weakened.

In order to achieve the above purpose, the technical scheme adopted in the application is as follows:

an ion source comprises a first support body, a second support body and an air flow pipeline, wherein the first support body and the second support body are arranged at intervals to form an ion channel, the first support body is provided with a needle electrode, the second support body is provided with an annular electrode, and the tip end of the needle electrode extends into the annular electrode; the gas flow conduit is directed toward the tip of the needle electrode for introducing helium gas to the needle tip.

An annular cavity surrounded by the annular electrode is used for introducing nitrogen.

In one embodiment, the needle electrode has a through hole inside that passes through to the needle tip to form an air flow conduit.

In one of the embodiments, the diameter of the annular cavity is 3-6 times the diameter of the air flow duct, preferably the diameter of the air flow duct is 0.5-1 mm, and the diameter of the annular cavity is 3-6 mm.

In one embodiment, the needle electrode is arranged concentrically with the ring electrode, and the tip of the needle electrode is located in the middle of the axis of the ring electrode;

the second support body is provided with a penetrating mounting hole, the hole wall of the mounting hole is provided with a metal conducting layer in a surrounding mode to form an annular electrode, and the second support body is provided with an air inlet pipe communicated with the annular cavity.

The high-field asymmetric waveform ion mobility spectrometry comprises a shell with an opening at one end, wherein a containing cavity of the shell is provided with a mobility pole plate group, a detection pole plate group and the ion source, and an ion channel faces to the opening;

the ion source, the migration polar plate group and the detection polar plate group are sequentially arranged from far to near in the direction away from the opening.

In one embodiment, the shell comprises two insulating plates which are arranged in parallel and spaced apart from each other, and a side plate arranged between the insulating plates, wherein the side plate partially surrounds the insulating plates, and an opening is formed in the shell;

the first support body and the second support body of the ion source are arranged oppositely and distributed on different insulating plates; the migration polar plate group comprises two migration polar plates which are oppositely arranged, and the two migration polar plates are distributed on different insulating plates; the detection polar plate group comprises two detection polar plates which are oppositely arranged, and the two detection polar plates are distributed on different insulating plates.

In one embodiment, the first support body and the corresponding insulating plate are of an integral structure, and the second support body and the corresponding insulating plate are of an integral structure.

In one embodiment, the distance between the two transfer plates is 0.2mm to 1mm and/or the distance between the two sense plates is 0.2mm to 1mm.

A method of improving resolution and sensitivity of a high field asymmetric waveform ion mobility spectrometry comprising the steps of:

by adopting the high-field asymmetric waveform ion mobility spectrometry, helium is introduced into the airflow pipeline, and nitrogen is introduced into the annular cavity of the annular electrode; wherein the flow rate of helium is 10-40% of the flow rate of nitrogen.

In one embodiment, the flow rate of helium is 0.25-1L/min and the flow rate of nitrogen is 1.5-2.25L/min.

When the ion source provided by the embodiment of the application is used for high-field asymmetric waveform ion mobility spectrometry, since the needle-shaped electrode is provided with the airflow pipeline, helium enters from the airflow pipeline, so that the periphery of the tip of the needle-shaped electrode is in a helium environment, and helium is easier to ionize than nitrogen, as helium is added, the discharge current shows an increasing trend, which indicates that more ions are ionized in the helium environment, and the ion concentration at the entrance of the migration zone is increased, so that the ion signal intensity is increased along with the increase of the ion concentration. Because helium is a lighter gas, ions are more likely to strike the migration plate in the migration zone to be lost after helium is mixed in nitrogen, but because the ions with increased ionization are larger than the ions lost by striking the migration plate, the overall ion signal intensity is enhanced, and thus, the resolution and the sensitivity of the high-field asymmetric waveform ion migration spectrum are improved at the same time.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required for the embodiments or the description of the prior art will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic structural diagram of an ion source according to an embodiment of the present disclosure;

fig. 2 is a schematic structural diagram of an ion source according to another embodiment of the present disclosure;

fig. 3 is an exploded view of a high-field asymmetric waveform ion mobility spectrometry according to an embodiment of the present disclosure;

fig. 4 is a schematic structural diagram of a high-field asymmetric waveform ion mobility spectrometry according to another embodiment of the present disclosure;

FIG. 5 is a schematic diagram of an exploded structure of the high field asymmetric waveform ion mobility spectrometry of FIG. 4;

FIGS. 6a-6d are the effect of helium addition on FAIMS spectra at different nitrogen flow rates, respectively;

FIGS. 7a-7d are graphs showing the effect of helium addition on compensation voltage at different nitrogen flow rates, respectively;

FIGS. 8a-8d are, respectively, the effect of helium addition on ion signal intensity at different nitrogen flow rates;

FIGS. 9a-9c are graphs showing an analysis of the effect of increasing helium on ion signal intensity, where (9 a) is the discharge current, (9 b) is the initial discharge voltage, and (9 c) is the current (signal) value;

FIGS. 10a-10b are FAIMS spectra at various gas flow rates, where (10 a) is pure nitrogen and (10 b) is nitrogen+helium;

FIG. 11 is a comparison of FAIMS spectra of helium and nitrogen at the same mixed gas flow rate;

FIG. 12 is an illustration of ionic strength and resolution of addition of different gases;

FIGS. 13a-13d are the effect of adding He on FAIMS spectra under different RF conditions, respectively;

FIGS. 14a-14b are diagrams of resolution at different radio frequency voltages; wherein (14 a) is the resolution of peak 1 and (14 b) is the bimodal separation;

FIGS. 15a-15c show the effect of helium on ion signal intensity at various radio frequencies, where (15 a) is peak 1, (15 b) is peak 2, and (15 c) is peak 3.

Reference numerals illustrate:

10. an ion source; 110. a first support body; 120. a second support body; 130. an air flow duct; 111. a needle electrode; 121. a ring electrode; 122. a mounting hole; 20. transferring the polar plate group; 30. detecting a polar plate group; 40. a housing; 210. a migration polar plate; 310. detecting a polar plate; 510. an opening; 410. an insulating plate; 420. a side plate; 411. an upper insulating plate; 412. and a lower insulating plate.

Detailed Description

In order to make the technical problems, technical schemes and beneficial effects to be solved by the present application more clear, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.

It will be understood that when an element is referred to as being "mounted" or "disposed" on another element, it can be directly on the other element or be indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or be indirectly connected to the other element.

It is to be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate or are based on the orientation or positional relationship shown in the drawings, merely to facilitate description of the present application and simplify description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be configured and operated in a particular orientation, and therefore should not be construed as limiting the present application.

Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present application, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.

The applicant has studied the FAIMS device after noticing that helium gas with lighter mass and smaller volume is doped into the existing FAIMS device on the basis of nitrogen gas serving as carrier gas, and the resolution is improved and the strength of ion signals is weakened, and further has found that although helium gas doping can improve the resolution, the mass of the helium gas is small, the molecular weight is low, the movement amplitude of ions is increased, the number of ions annihilated on a polar plate is increased, and in addition, the diffusion movement is increased, ions are damaged, so that the resolution is improved and the strength of ion signals is weakened.

Based on the above-mentioned problems found by the applicant, the applicant has improved the structure of the ion source, and examples of the present application are further described below.

For a better understanding of the present application, embodiments of the present application are described below in connection with fig. 1 to 5.

Referring to fig. 1-2, an embodiment of the present application provides an ion source 10, including a first support body 110, a second support body 120 and an air flow pipe 130, where the first support body 110 and the second support body 120 are arranged at intervals to form an ion channel, the first support body 110 is provided with a needle electrode 111, the second support body 120 is provided with an annular electrode 121, and a tip end of the needle electrode 111 extends into the annular electrode 121; the gas flow conduit 130 is directed toward the tip of the needle electrode 111 for introducing helium gas to the needle tip.

It is to be appreciated that the ion source 10 can include a housing having at least one opening, and that the first support 110 and the second support 120 can be opposing walls of the housing. The aperture is an outflow aperture for ions generated by the ion source 10. When other devices are used, the openings are only required to face the ion target region, for example, in a high-field asymmetric waveform ion mobility spectrometry, the openings face the direction of the mobility plate group 20 and the detection plate group 30.

Of course, the ion source 10 itself may not be provided with a housing. When the ion source 10 is applied to other devices, the ion source 10 is disposed in the housing 40 of the other devices, the first support 110, the second support 120 and the housing 40 enclose to form an ion flow channel, and the ion flow channel faces the direction of the migration pole plate group 20 and the detection pole plate group 30, as in the high-field asymmetric waveform ion mobility spectrometry, the ion source 10 can be reasonably arranged.

An annular cavity surrounded by the annular electrode 121 is used for introducing nitrogen. The first support 110 and the second support 120 are disposed opposite to each other at a certain distance from each other, such as parallel or at an angle. The space between the first support 110 and the second support 120 is an ion channel, and ions generated by ionization of nitrogen and helium may flow along the space between the first support 110 and the second support 120.

The first support 110 and the second support 120 are used to fix the needle electrode 111 and the ring electrode 121, respectively. The shape and size of the first and

second supports

110 and 120 are not particularly limited, and a plate having a relatively thin thickness may be used to facilitate the installation of the corresponding electrodes. The first and

second supports

110 and 120 may be an insulating material such as PVC.

The annular electrode 121 may be embedded in the second support 120, for example, the second support 120 is provided with a through annular cavity, and the wall of the cavity is surrounded by electrode material to form the annular electrode 121. The nitrogen source can be communicated with the annular cavity, and nitrogen is introduced. The ring electrode 121 may also be disposed outside the second support 120 in an extending manner, for example, the second support 120 has a hollow cylinder protruding from a surface, the hollow cylinder penetrates through the second support 120, and an electrode material surrounds an end portion of the second support 120 away from the second support to form the ring electrode 121. The nitrogen source can be communicated with the hollow cylinder body, and nitrogen is introduced. The nitrogen source may be in communication with the hollow cylinder via a conduit.

Referring to fig. 1-2, the tip of needle electrode 111 protrudes into ring electrode 121. The gas flow pipe 130 has one end communicating with an external helium source and the other end directed toward the tip of the needle electrode 111, and introduces helium gas near the tip of the needle electrode 111. The air flow pipe 130 may be a metal pipe such as a steel pipe, a copper pipe, etc., or a non-metal pipe such as a plastic pipe, a rubber pipe, etc. A non-metallic tube is preferred to reduce interference with the discharge between needle electrode 111 and ring electrode 121. Helium is introduced near the tip of the needle electrode 111 such that the tip of the needle electrode 111 is surrounded by a helium atmosphere, and helium is more easily ionized than nitrogen, and thus, as helium is added, the discharge current tends to increase. It is shown that more ions are ionized in the helium environment and the ion concentration at the entrance of the migration zone increases, so that the ion signal intensity increases with the increase of the ion concentration. Since helium is a relatively light gas, ions are more likely to strike the transfer plate 210 in the transfer region to be lost after mixing helium in nitrogen, but since the ions with increased ionization are larger than those lost by striking the transfer plate 210, the overall ion signal intensity is enhanced, thus improving the resolution and sensitivity of the high-field asymmetric waveform ion mobility spectrum at the same time.

Referring to fig. 1, in one embodiment, needle electrode 111 has a through hole inside that passes through to the needle tip to form an air flow duct 130.

In this embodiment, the needle electrode 111 has a hollow structure, and the air flow duct 130 is integrated in the middle of the needle electrode 111, penetrating through to the needle tip. Needle electrode 111 may be a disposable sterile syringe needle for medical use. The end far away from the needle point is communicated with helium gas, and the helium gas is led into the needle point. Helium directly flows out from the needle point, the obstruction of nitrogen needs to be overcome to be small, the needle point can be surrounded at a low flow rate, and a helium atmosphere is provided. Helium flows out from the end face of the needle tip, so that the concentration distribution of the helium around the needle tip is relatively uniform. In addition, the air flow pipeline 130 is integrated in the middle of the needle electrode 111, so that the whole device has high integration level, simple structure and reduced volume.

Preferably, the gas flow conduit 130 is disposed at the axial center of the needle electrode 111, and the helium concentration distribution around the needle tip is more uniform.

Referring to fig. 1, in one embodiment, the diameter of the annular cavity is 3 to 6 times the diameter of the air flow duct 130, preferably the diameter of the air flow duct 130 is 0.5 to 1mm, and the diameter of the annular cavity is 3 to 6mm.

Referring to fig. 1, in one embodiment, the needle electrode 111 is disposed concentrically with the ring electrode 121, and the tip of the needle electrode 111 is located in the center of the axis of the ring electrode 121; the second support 120 is provided with a through mounting hole, the hole wall of the mounting hole is provided with a metal conducting layer in a surrounding mode to form an annular electrode 121, and the second support 120 is provided with an air inlet pipe mounting hole communicated with the annular cavity.

The wall body of the second support body 120 is provided with a penetrating mounting hole, the hole wall of the mounting hole is provided with a metal conducting layer in a surrounding mode to form an annular electrode 121, the annular electrode 121 is integrally arranged on the wall body of the second support body 120, the total thickness of the annular electrode 121 and the second support body 120 is reduced, and the structure is also more simplified.

Referring to fig. 3 to 5, a high-field asymmetric waveform ion mobility spectrometry includes a housing 40 having an opening 510 at one end, a containing cavity of the housing 40 is provided with a mobility plate group 20, a detection plate group 30 and the ion source 10, and an ion channel faces the opening 510; the ion source 10, the transfer plate group 20, and the detection plate group 30 are disposed in this order from the far side to the near side in a direction away from the opening 510.

The ion source 10 is an ionization region in the region of the housing 40, the migration plate group 20 is a migration region in the region of the housing 40, and the detection plate group 30 is a detection region in the region of the housing 40.

The ion source 10 includes a needle electrode 111 and a ring electrode 121, and after the sample gas is ionized into charged ions in the ionization region, the carrier gas carries it into the migration region. The migration pole plate group 20 comprises two migration pole plates 210 which are oppositely arranged, and the two migration pole plates 210 can be added with high-voltage asymmetric waves with the frequency of 1MHz and the duty ratio of 30% and compensation voltages with the scanning range of-13V to 13V. After charged ions which do not meet the experimental requirements are filtered out in the migration area, the rest ions reach the detection area, the detection area comprises two detection polar plates 310 which are arranged oppositely, 9V voltage is applied to the two detection polar plates 310, so that the ions can deflect to reach the detection substrate, and then the ions are detected by a subsequent weak current detector, and the detected weak signal value is uploaded to the microprocessor controller.

Because the ion source 10 is adopted, the ionized ions are larger than the ions lost by the impact migration polar plate 210, so that the overall ion signal strength is enhanced, and the resolution and the sensitivity of the high-field asymmetric waveform ion mobility spectrometry are improved.

In one embodiment, referring to fig. 3 to 5, the case 40 includes two insulating plates 410 arranged in parallel and spaced apart from each other, and a side plate 420 disposed between the insulating plates 410, the side plate 420 partially surrounding the insulating plates 410, and an opening 510 is formed in the case 40; the first support 110 and the second support 120 of the ion source 10 are disposed opposite to each other and distributed on different insulating plates 410; the migration pole plate group 20 comprises two migration pole plates 210 which are oppositely arranged, and the two migration pole plates 210 are distributed on different insulating plates 410; the sensing electrode plate set 30 includes two sensing electrode plates 310 disposed opposite to each other, and the two sensing electrode plates 310 are distributed on different insulating plates 410.

The two transfer plates 210 may be two oppositely disposed copper-clad electrodes, each of which is disposed on an insulating plate 410. Likewise, the two sensing pads 310 may be two oppositely disposed copper-clad electrodes, each of which is disposed on an insulating plate 410. The first support body 110 is fixed on one insulating plate 410, and the second support body 120 is fixed on the other insulating plate 410.

In one embodiment, referring to fig. 3 to 5, the first support body 110 is in a unitary structure with the corresponding insulating plate 410, and the second support body 120 is in a unitary structure with the corresponding insulating plate 410. The design uses an insulating plate 410 as a first support 110 and another insulating plate 410 as a second support. The whole device has higher integration level and more simplified structure.

In one embodiment, referring to fig. 3-5, the distance between two transfer plates 210 is 0.2 mm-1 mm, and/or the distance between two sense plates 310 is 0.2 mm-1 mm.

helium is introduced into the gas flow pipeline 130, and nitrogen is introduced into the annular cavity of the annular electrode 121 by adopting the high-field asymmetric waveform ion mobility spectrometry; wherein the flow rate of helium is 10-40% of the flow rate of nitrogen.

The following describes the technical scheme of the present application with reference to specific embodiments.

Experimental device

The FAIMS experiment platform consists of a sample injection module (a helium unit and a sample injection unit), a FAIMS device, a weak current detector, a power supply module, a microprocessor controller and a spectrogram display module. The carrier gas used in the experiment is high-purity nitrogen and high-purity helium (99.999% produced by Guangxi Ruida chemical engineering Co., ltd.), the flowmeter is a D08-1F type flow indicator and a CS200A digital gas mass flow controller (produced by Beijing seven-star Hua Chuang electronic Co., ltd.), and the measurable gas flow range is 0-5L min ^-1 The adjusting precision is 0.01L min ^-1 The method comprises the steps of carrying out a first treatment on the surface of the The test sample was untreated volatile organic ethanol (CH 3CH2OH, 99.7% of the chemical company, inc.), and the test was carried out at normal temperature and pressure.

The small flask with the ethanol sample is placed in a sample cell (height 4cm, diameter 3.5 cm), the whole sample unit is connected by a gas pipe through a pneumatic interface, and carrier gas helium is introduced to enable the sample to be carried into an ionization region of the FAIMS device by the helium.

Design and manufacture of FAIMS device

As shown in fig. 1, for convenience of description, two insulating plates 410 are defined as an upper insulating plate 411 and a lower insulating plate 412. The upper insulating plate 411 and the lower insulating plate 412 are manufactured by using a PCB technology, and the insulating plates 410 are sealed by using a PCB soldering process. The device adds a helium ventilation device on the FAIMS system board based on the brazing process, wherein the sizes of the upper insulating board 411 and the lower insulating board 412 are respectively 60mm multiplied by 40mm and 60mm multiplied by 55mm, and a gasket of 0.2mm is placed between the upper insulating board 411 and the lower insulating board 412. The upper insulating plate 411 is composed of a hole of 1mm diameter and two copper-clad electrodes, and the lower insulating plate 412 is composed of a hole of 3mm diameter and two copper-clad electrodes (sizes 15mm×10mm and 10mm×8 mm) for use as the migration zone plate and the detection plate 310, respectively.

The needle-ring discharge structure is used as the ion source 10, and after the sample gas is ionized into charged ions in the ionization region, the carrier gas carries it into the migration region, to which high-voltage asymmetric waves with a frequency of 1MHz and a duty ratio of 30% and compensation voltages with a scanning range of-13V to 13V are applied. After charged ions which do not meet the experimental requirements are filtered out in the migration zone, the rest ions reach the detection zone, 9V of voltage is applied to the deflection substrate of the detection zone, so that the ions can deflect to reach the detection substrate, the ions are detected by a subsequent weak current detector, and the detected weak signal value is uploaded to the microprocessor controller.

Hollow needle-ring ion source

In order to improve the resolution and sensitivity of FAIMS, a ventilating structure with helium and nitrogen opposite to each other is designed, and an ionization region is formed by a needle-ring electrode. The needle electrode 111 is hollow, and helium gas enters the ionization region from the hollow portion of the needle electrode 111, in this way, helium gas can pass through the hollow needle electrode 111 to surround the needle tip with helium gas, which can increase discharge current of the tip and improve ionization efficiency. Needle electrode 111 is medical disposable aseptic syringe needle, and hollow internal diameter is 0.26mm, and the external diameter is 0.5mm, and length 60mm, needle's fixed knot constructs adopts PLA polylactic acid material to pass through 3D and prints to form, and two big cylinders that diameter is 16mm from top to bottom pass through 8mm, and the bottom surface diameter is 3mm little cylinder combination forms, designs on needle's fixed knot constructs and upper insulation board 411 that diameter 1mm aperture is passed through with the hollow needle, and helium lets in from the hollow needle, guarantees simultaneously that the hollow needle is in the annular electrode 121 centre. Copper is coated on the 3mm hole of the lower plate to serve as a discharge anode, and the discharge anode and the hollow needle of the upper plate are combined to form an ionization source, and in the experimental process, nitrogen carries a sample to enter the needle-ring ionization source from the 3mm hole of the lower insulating plate 412 for ionization. In order to ensure air tightness, a nitrogen gas sampling device made of red copper is designed and manufactured, and the nitrogen gas sampling device consists of cylinders with the inner diameter and the outer diameter of 16mm and 10mm respectively and is directly connected with a polytetrafluoroethylene tube with the outer diameter of 4mm through a pneumatic connector.

The needle electrode 111 is connected to the negative pole of the negative dc high voltage power supply through a 6mΩ ballast resistor for limiting the discharge loop current and suppressing spark discharge, and the ring electrode 121 is connected to the ground of the negative dc high voltage power supply through a 1kΩ test resistor. And an oscilloscope and a universal meter are loaded at two ends of the test resistor and used for obtaining a discharge waveform and a discharge current generated by the discharge of the needle-ring asymmetric electrode, and the range of a negative direct current high voltage power supply (HB-F203-5 AC) is 0 to-20 kV.

Fourth, experimental results

4.1 increasing ion Signal Strength and resolution

Under the conditions of discharge voltage-2 kV, ballast resistor 6M, radio frequency voltage 300V and ethanol as a sample, different N ₂ Adding at flow rate for 0.2L min ^-1 ，0.3L min ^-1 ，0.5L min ^-1 ，1L min ^-1 He in He is shown in table 1. With N ₂ Increasing flow rate, decreasing He ratio at the same flow rate, when N ₂ He is 1L min ^-1 In this experiment, the He ratio was 50% and was in the range of 0 to 50% because He ratio was the maximum, and this range considered the breakdown characteristic of He and was the safe range for the experiment.

TABLE 1 helium ratios at different nitrogen flows

FIGS. 6 (a-d) are N respectively ₂ The flow rate is 1L min ^-1 ，1.5L min ^-1 ，2L min ^-1 ，2.5L min ^-1 Under the condition of adding differentFAIMS spectra of He ratios. From the figure, it can be seen that different N ₂ Increasing the ratio of He at flow rates can increase the separation capacity of the FAIMS spectrum and increase the ionic peak intensity, and it is generally believed that the offset voltage peak with the greater offset is the monomer peak, and then the dimer peak, and the offset is the polymer peak, where the three peaks are designated as peak 1, and peak 3. Taking FIG. 6c as an example, when N ₂ The flow rate was 2L/min, the He ratio was 9%, and the peak 1 ion signal intensity reached a maximum of 33.45pA. The He ratio was increased to 20% and the number of ion peaks was changed from the original two to three. The ratio of He is continuously increased to 33%, and the signal intensity is reduced, but is 1.56 times larger than that when He is not added, and the separation of three peaks is more and more obvious, so that the ion type separation effect is better and the signal intensity is improved along with the increase of the ratio of He.

Fig. 7 (a-d) are graphs showing the compensation voltage positions of the FAIMS spectra, and it is understood that the compensation voltage positions of the

peaks

1,2, and 3 are changed with the increase of the He ratio. Taking fig. 7a as an example, as the He ratio increases, the positions of the

peaks

1 and 2 shift downward, and the position of the peak 3 shifts upward, and the amplitude of the downward shift of the peak 1 is greater than that of the peak 2, so that the distances between the three peaks are originally greater.

Resolution may be expressed in terms of peak width of the monomer peaks, degree of separation between different peaks or difference in compensation voltage between three peaks. The larger the distance between the compensation voltages, the higher the resolution, and vice versa, the resolution gradually decreases. It can be seen from the figure that at different N ₂ At the flow rate, as the He ratio increases, the resolution increases.

To more intuitively and clearly see the compensation voltage difference between the peak 1 and the peak 2 and between the peak 2 and the peak 3, different N in FIG. 7 are shown ₂ The effect of applying He at flow rate on the compensation voltage is expressed numerically as shown in tables 2, 3 (where "-" indicates that peak 3 has not yet occurred). Table 2 shows the difference in compensation voltage between peak 1 and peak 2, at the same N ₂ As the He ratio increases under the flow, the difference between the compensation voltages can be seen to increase gradually, and the degree of separation between peak 1 and peak 2 is also higher and higher; in Table 3, there is no difference between peak 2 and peak 3, which isSince peak 3 has not yet appeared under this condition, peak 3 appears with increasing He ratio and the distance from peak 2 is larger and larger, the degree of separation between peak 2 and peak 3 is higher and higher, so that it is verified again that the resolution increases with increasing He ratio.

TABLE 2 Compensation Voltage comparison between Peak 1 and Peak 2

TABLE 3 Compensation Voltage comparison between Peak 2 and Peak 3

The formula for calculating the compensation voltage is as follows:

wherein K is _h And K _l Ion mobility under high and low field conditions, respectively, g is the distance between the transfer plates, d is a given single radio frequency duty cycle, E _pp For a single radio frequency high voltage amplitude, d _H Is a high field duty cycle.

The Brownian theorem considers that the ion mobility of a mixed carrier gas is related to the ratio of the mixed gas and the nonlinear variation thereof is far more than the ion mobility variation under a single gas, and the value of the compensation voltage is changed along with the ion mobility variation, as can be seen from the above formula, (K) _h -K _l ) The larger the value of the compensation voltage is, and the experimental phenomenon is consistent with the theoretical research.

FIGS. 8 (a-d) are N ₂ The flow rates are respectively 1L min ^-1 ，1.5L min ^-1 ，2L min ^-1 ，2.5L min ^-1 Ion signal intensity maps of different He ratios were added. As can be seen from the graph, when the He proportion is small, the peak 3 does not appear, the ion signal intensity of the three peaks basically shows a trend of increasing and then decreasing with the increase of the He proportion, and the peak 1 and the peak 2 are respectively at 0.2 and 0.3L min ^-1 The peak at He reached a maximum and then decreased.

FIGS. 9 (a-c) are pair wise increasesThe helium flow can improve the analysis of the ion signal intensity, and the experimental condition is that the nitrogen flow is 1.5L min ^-1 The ballast resistor is 6MΩ, under the action of negative DC high voltage, the needle-ring electrode generates corona discharge and glow discharge, and the discharge current in the circuit is an important parameter for representing the severity of the discharge. As shown in FIG. 9a, the discharge current connected to the 1KΩ test resistor was observed under the discharge voltage of-2 KV, and it was found from the graph observation that the nitrogen flow was 1.5L min ^-1 While the application of nitrogen on the basis of the same proportion of helium has no effect on the discharge current, the discharge current is gradually increased, the increase in current value being probably due to more sample ions being ionized as helium is added to the ionization region. Fig. 9b shows the effect of He on the initial discharge voltage, as can be seen, the nitrogen gas is continuously added on the basis of the nitrogen gas, and the increase of helium gas decreases the initial discharge voltage. Fig. 9c shows the effect of adding helium gas with different flow rates on the intensity of the ion signal without applying the radio frequency voltage under the condition of continuously scanning the compensation voltage, and the effect can be seen that the ion signal is stronger as the helium gas increases, so that more ions in the ionization region are ionized along with the increase of the helium gas flow rate.

The ionic signal intensity calculation formula is as follows:

wherein: n is n _in For ion concentration at the entrance of the migration zone, Q is carrier gas flow, t _res For the time of the ion passing through the migration zone, D is the diffusion coefficient of the ion, g _e K is the effective distance of the migration zone _B Is Boltzmann constant, q is ion charge number, g is migration zone substrate spacing, T is Kelvin temperature, V _H The amplitude of the square wave radio frequency voltage is d is the duty cycle, and f is the frequency of the square wave radio frequency voltage.

With the addition of He, the discharge current shows an increasing trend, which indicates that more ions are ionized in the environment of He, and the ion concentration n at the entrance of the migration zone _in As can be seen from the above equation, the signal intensity H follows the ion concentration n _in Is increased by (a)And increases. Since He is a relatively light gas, in N ₂ Ions are more likely to strike the transfer plate 210 in the transfer region and are lost after He is mixed, and when ions due to increased ionization are larger than ions lost by striking the transfer plate 210, the ion signal intensity is increased, and conversely, is decreased, which explains why the ion signal intensity is increased and then decreased after the helium ratio is increased. In the flat-plate FAIMS in the early test of the invention, nitrogen and helium are mixed before entering an ionization region, and after helium is added, the ionization efficiency of an ion source cannot be improved, but the movement amplitude is increased in a migration region due to the improvement of the ion mobility, and the probability of the ions being impacted on a substrate and annihilated due to diffusion, space charge effect and the like is increased, so that signals are reduced.

4.2 flow control experiments

To exclude the effect of increasing helium on FAIMS spectra due to flow increases, the following control experiments were performed: at N ₂ The flow rate is 2L min ^-1 Under the condition of (1) adding a group of doping gases for 0.2L min ^-1 ,0.3Lmin ^-1 ,0.5L min ^-1 And 1L min ^-1 Another group of control group of doping gases is added with N with the same flow rate ₂ Two sets of FAIMS spectra were observed for changes. FIG. 10 (a-b) shows FAIMS spectra obtained under the conditions of radio frequency voltage 200V, ballast resistor 6M, discharge voltage-2 KV, as seen in FIG. 10a, at 2L min ^-1 Gradually increasing N on the basis of ₂ Only has influence on the signal intensity, the value of the compensation voltage is not influenced, the curve peak width is gradually widened, and the resolution ratio is reduced; FIG. 10b is at N ₂ Is 2L min ^-1 Based on the increasing He, the compensation voltage shifts leftwards as the proportion of He increases, the signal intensity increases and then decreases, and the peak 2 appears gradually, thus improving the resolution.

At initial N ₂ The flow rate is 2L min ^-1 Under the condition of adding N with the same flow rate into the mixed gas ₂ And He are put together for comparison as shown in fig. 11. Observed increase of 0.3L min ^-1 He and increase 0.3L min ^-1 N ₂ The graph of (a) shows that the signal intensity, the compensation voltage value and the wave crest number are all differentAnd the same is true. At a total flow rate of 2.3L min ^-1 Under the condition of adding 0.3L min ^-1 The peak signal intensity of the ion after helium is 197.3pA, which is 0.3L min added ^-1 At the same time, the compensation voltage is increased from-1.98V to-2.37V at the signal intensity of 70pA 2.83 times of the nitrogen, and the same is true in other flow rate cases, which shows that the experimental phenomenon caused by increasing the He proportion is not caused by the flow rate increase only.

FIG. 12 is at N ₂ The flow rate is 2L min ^-1 At the time, 0L min is added respectively ^-1 ,0.2L min ^-1 ,0.3L min ^-1 ,0.5L min ^-1 ,1L min ^-1 N of (2) ₂ He ion intensity and resolution contrast plot. As can be seen, with N ₂ The ion signal intensity increased gradually from the original 52.76pA to 85.68pA and only one peak, the increase in signal intensity being due to the flow rate. With the increase of the proportion of the added He, the ion signal intensity is increased and then decreased, 0.3L min is added ^-1 The He signal strength reaches 197.26pA, which is increased by 0.3L/min ^-1 N ₂ 2.83 times the signal strength and under this condition a second peak of amplitude 15.22pA occurs, which is due to the improved resolution.

The resolution calculation formula for peak 1 is as follows:

wherein V is _H Is the amplitude of square wave radio frequency voltage, K _L For ion mobility under low electric field conditions, α (E/N) is the ion mobility coefficient, d is the duty cycle, k _B Is Boltzmann constant, T is Kelvin temperature, q is ionic charge, T _res The time for the ions to pass through the transition region, R is the resolution, CV is the compensation voltage value, and FWHM is the half-width.

From the above, it can be seen that as N ₂ An increase in the flow rate, time t of ion passage through the migration zone _res And decreases, resulting in a decrease in resolution. At 2L min ^-1 N ₂ The resolution is gradually increased by gradually adding He under the condition that He is a relatively light gas, along with HeThe increase in (2) accelerates the oscillation of ions in the transition zone, thereby improving ion resolution, and the control experiment verifies that the effect of He addition on FAIMS spectra is not due to the increase in flow rate.

4.3 different radio frequency conditions

At discharge voltage-2 kV, ballast resistor 6MΩ, N ₂ Flow rate 2L min ^-1 Fig. 13 (a-d) are FAIMS spectra of different He flow rates applied at 200v,250v,300v,350v radio frequency, respectively. As can be seen from the graph, under different radio frequency conditions, as the ratio of He increases, the ion signal intensity increases and then decreases, but the total signal intensity is smaller or larger than that of He. Taking FIG. 13b as an example, when increasing He to 0.2L min ^-1 I.e., 9% helium (corresponding to Table 1), the signal intensity of peak 1 increased from 26.82pA without He addition to 84.75pA by a factor of 3.15. Continuing to increase He, gradually decreasing the signal intensity, and when the He proportion reaches the N ₂ At 33% of the maximum value at the flow rate, the ion signal intensity was reduced to 61.37pA, but it was still 2.29 times greater than that without He addition. At the same time, the same rule is observed for peak 2 of FIG. 13b, when He is not added, the ion signal intensity of peak 2 is only 4.02pA, and when He is added, the ion signal intensity is 0.3 Lmin ^-1 He reached 8.36pA, and then decreased to 5.9pA, but was still greater than 4.02 pA. This experimental phenomenon demonstrates that increasing He can increase the sensitivity (signal intensity) of ions. The calculation formula of the degree of separation between the two peaks is as follows:

wherein R is ₁ Degree of separation, CV, being bimodal ₁ And CV (constant velocity) ₂ Compensation voltage values of peak 1 and peak 2, respectively, W ₁ And W is equal to ₂ Peak widths of peak 1 and peak 2, respectively.

FIG. 14a shows the peak 1 resolution calculated by the formula under different RF conditions, and it can be seen from the graph that as the ratio of He increases, the peak width becomes narrower, the compensation voltage becomes larger, the resolution of the monomer peak increases, and 1L min is added under the conditions of 200V,250V,300V,350V of RF ^-1 When He, the resolution reaches the highest, 1.61,1.90 is respectively improved by less He addition,1.61,2.34 times. Fig. 14b shows the degree of separation between

peaks

1 and 2 calculated by the formula under the conditions of rf voltages 250v,300v,350v, and the degree of separation between peaks is greater and greater with increasing He ratio, further improving resolution. As can be seen from fig. 14a, when the rf voltage is 200v and the He ratio is 13%, a double peak appears, but since the peak 2 is not completely separated from the peak 1, it is difficult to calculate the specific separation degree by the formula, and increasing He causes the appearance of the second peak, and from another angle, it is proved that increasing He can improve the resolution; when the radio frequency voltage is 300v and 350v respectively, a third peak appears gradually along with the increase of the proportion of He, which also shows that the resolution increases gradually along with the addition of He, and in addition, the larger the radio frequency voltage, the larger the resolution increase amplitude after the addition of helium. When the radio frequency voltage is 200V,250V,300V and 350V, the resolution of the monomer peak is respectively increased from 2.13 to 3.42, from 2.67 to 5.09, from 3.39 to 6.55, from 5.31 to 12.43, and the increase multiple is 1.61,1.91,1.93,2.34. When the radio frequency voltage is 250V,300V and 350V, the bimodal separation degree is respectively increased from 1.57 to 2.6, from 2.33 to 4.37, from 4.17 to 9.51, and the increase multiple is 1.66,1.88,2.28.

Fig. 15 (a-c) are graphs of signal intensity changes of peak 1, peak 2 and peak 3 with increasing He ratio under different radio frequency conditions, respectively, and it can be seen that with increasing He ratio, the signal intensities of peak 1, peak 2 and peak 3 all have a tendency to increase and decrease first and then, but the peak can reach the maximum under different He ratios. When the radio frequency voltage is 200V, the flow rate of He is 0.3L min for peak 1 and peak 2 ^-1 Maximum is reached. Continuing to increase He, the signal intensity decreases, but is still greater than without He addition, at which point peak 3 has not yet occurred. When the RF voltage is 300V, peak 1 is at 0.2L min ^-1 The signal value is the largest at He, and the peak 2 is 0.3L min ^-1 The peak value at He is highest, and peak 3 is 0.5L min ^-1 He occurs and reaches a maximum at this radio frequency condition, with a subsequent peak reduction. In summary, increasing He increases sensitivity under different rf conditions, and the effect of rf voltage on sensitivity is directly opposite to that of resolution. For peak 1, the smaller the RF voltage amplitude, the more pronounced the effect of increasing helium on signal strength, when the RF voltage is 200V, adding 0.3L min ^-1 The highest signal intensity can be increased by 3.74 times when helium gas, and the signal intensity can be increased by 1.7 times when the radio frequency voltage is 350V; the change rule of the signal intensity of the peak 2 and the peak 3 is similar, but the peak 2 and the peak 3 can be generated only by adding more helium under the condition of higher radio frequency voltage or the same voltage.

The experimental result shows that the method is carried out in 1L min ^-1 ,1.5L min ^-1 ,2L min ^-1 and 2.5L min ^-1 N ₂ At the flow rate, the addition of He increases the value of the offset voltage, the number of ion peaks changes from two to three, and the offset voltage distance between different ion peaks increases, indicating an increase in the resolution of FAIMS. On the other hand, the signal intensity of the ion peak was also improved, indicating that the sensitivity of FAIMS was also improved, and the flow rate of nitrogen gas was 2L min ^-1 Under the condition of adding helium and nitrogen with the same flow as mixed carrier gas, so that the total flow is the same, and experiments of adding helium under different radio frequency voltages also prove that the resolution and the sensitivity of FAIMS can be improved simultaneously by adding helium.

The foregoing description of the preferred embodiment of the present invention is not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Claims

1. The ion source is characterized by comprising a first support body, a second support body and an air flow pipeline, wherein the first support body and the second support body are arranged at intervals to form an ion channel, the first support body is provided with a needle electrode, the second support body is provided with an annular electrode, and the tip end of the needle electrode stretches into the annular electrode; the airflow pipeline points to the tip of the needle-shaped electrode and is used for introducing helium gas to the needle tip; the annular cavity is surrounded by the annular electrode and is used for introducing nitrogen; the needle electrode is internally provided with a through hole penetrating to the needle point to form the air flow pipeline; the needle-shaped electrode and the annular electrode are concentrically arranged, and the tip end of the needle-shaped electrode is positioned in the middle of the axis of the annular electrode; the second support body is provided with a penetrating mounting hole, a metal conducting layer is arranged around the hole wall of the mounting hole to form the annular electrode, and the second support body is provided with an air inlet pipe communicated with the annular cavity.

2. The ion source of claim 1, wherein the annular cavity has a diameter of 3-6 times the diameter of the gas flow conduit, the gas flow conduit has a diameter of 0.5-1 mm, and the annular cavity has a diameter of 3-6 mm.

3. A FAIMS device comprising a housing having an opening at one end, a receiving cavity of the housing provided with a set of transfer plates, a set of detection plates, and the ion source of any one of claims 1-2, an ion channel facing the opening; the ion source, the migration polar plate group and the detection polar plate group are sequentially arranged from far to near in the direction away from the opening.

4. A FAIMS device according to claim 3, wherein the housing comprises two insulating plates arranged in parallel and spaced apart a distance and a side plate disposed between the insulating plates, the side plate partially surrounding the insulating plates, an opening being formed in the housing; the first support body and the second support body of the ion source are arranged opposite to each other and distributed on different insulating plates; the migration polar plate group comprises two migration polar plates which are oppositely arranged, and the two migration polar plates are distributed on different insulating plates; the detection polar plate group comprises two detection polar plates which are oppositely arranged, and the two detection polar plates are distributed on different insulating plates.

5. The FAIMS device of claim 4, wherein the first support is of unitary construction with the corresponding insulator plate and the second support is of unitary construction with the corresponding insulator plate.

6. The FAIMS device of claim 4, wherein the distance between the two displacement plates is between 0.2mm and 1mm and the distance between the two detection plates is between 0.2mm and 1mm.

7. A method of improving resolution and sensitivity of a FAIMS device comprising the steps of: introducing helium into the airflow pipeline and introducing nitrogen into the annular cavity of the annular electrode by adopting the FAIMS device as claimed in any one of claims 4 to 6; wherein the flow rate of the helium gas is 10-40% of the flow rate of the nitrogen gas.

8. The method of claim 7, wherein the helium flow is 0.25-1L/min and the nitrogen flow is 1.5-2.25L/min.